1. Field of the Invention
Aspects of the present invention relate to a center pin for a secondary battery and a secondary battery having the same, and more particularly, to a center pin for a secondary battery, which can optimize the void volume of the secondary battery.
2. Description of the Related Art
In recent times, various handheld, electronic devices, such as cellular phones, notebook computers, camcorders, and so on, have been developed and manufactured. Handheld electronic devices generally include a secondary battery for portable operations. Exemplary secondary batteries include nickel-cadmium (Ni—Cd) batteries, nickel-metal hydride (Ni-MH) batteries, and lithium (Li) batteries.
Lithium secondary batteries are widely employed in portable electronic devices, because they have three times the operating voltage and a higher energy density per unit weight than the Ni—Cd batteries and the Ni-MH batteries. A lithium secondary battery may be classified as a lithium ion battery, which uses a liquid electrolyte, or as a lithium polymer battery, which uses a polymer electrolyte. A secondary battery may also be classified as a rectangular, cylindrical, or pouch-type, according to the shape thereof.
A cylindrical secondary battery generally includes: a cylindrical, wound, electrode assembly; a center pin disposed in the electrode assembly; a can to house the electrode assembly; an electrolyte to transfer lithium ions in the electrode assembly; and a cap assembly to seal the can. The electrode assembly includes: a positive electrode plate having a positive electrode collector, to which a positive electrode active material is applied; a positive tab that extends from one side of the positive electrode collector; a negative electrode plate having a negative electrode collector to which a negative electrode active material is applied; a negative electrode tab that extends from one side of the negative electrode collector; and a separator disposed between the positive electrode plate and the negative electrode plate.
Lithium ions, generated by electrochemical reactions in the electrode assembly, are transferred through the electrolyte during charging or discharging of the secondary battery. The electrolyte may be a non-aqueous organic electrolyte, which is a mixture of a lithium salt and a high-purity organic solvent, or may be a polymer electrolyte.
The cap assembly includes a safety vent that is deformed, or broken, by gas generated during an abnormal operation of the electrode assembly. The safety vent prevents the cylindrical secondary battery from combusting or exploding, due to damage to overcharging, over discharging, or external impacts to the secondary battery.
The center pin prevents the deformation of the electrode assembly, during the charging or discharging, and provides a passage for the release of the gas. Thus, the gas can be channeled to the safety vent, which can then deform or break, such that the secondary battery does not combust or explode.
The secondary battery has a certain amount of empty space (void volume). However, as the center pin includes a hole formed in a longitudinal direction in the center pin in a direction of the cap assembly, so that a void volume of the secondary battery is increased, the insulating and charging characteristics of the secondary battery may be degraded, and the deformation or breakage of the safety vent may be delayed.
Moreover, when the separator of the electrode assembly includes a ceramic porous layer to enhance the characteristics of the secondary battery, the void volume in the secondary battery becomes much larger. Thus, the deformation or breakage of the safety vent is delayed, and the secondary battery can combust or explode.
However, if the center pin does not have a hole therein, or all volume of the hole is sealed by a sealing member, the void volume of the secondary battery is greatly reduced by the sealed volume of the hole, and thus, the high-temperature storage characteristics of the secondary battery can be degraded.